Speaking at a news conference on Friday, the coach said it would be "impossible" to lose Willian, and the club are keen to ensure he is as well-equipped as possible for what is set to be a close battle for a top-four spot.

Barcelona made a concerted effort to sign Willian in the summer, and sources close to the player have told ESPN FC that he believes they remain interested.

He has 18 months left on his Chelsea contract and has yet to begin talks about an extension.

Sarri's wing options have been bolstered by the return to fitness of both Willian and Pedro from muscle injuries, but uncertainty surrounding Callum Hudson-Odoi's future makes Willian's availability all the more important.

Earlier this week, sources told ESPN FC that Chelsea were prepared to report Bayern Munich to FIFA if evidence of an illegal approach to Hudson-Odoi was found.

Bayern sporting director Hasan Salihamidzic said on Wednesday that the Bundesliga champions "absolutely want to sign" Hudson-Odoi, and sources have told ESPN FC that they are increasingly confident of completing a deal.